Opacified polymer composition

ABSTRACT

There is disclosed a polymer composition comprising a polymer resin and, as opacifier, a flash calcined kaolin clay filler and a TiO 2 . The polymer composition may be formed into shaped articles, particularly polyolefin film.

FIELD OF THE INVENTION

This invention relates generally to the use of a flash calcined kaolinclay as an opacifier for a polymer composition, and more particularly tothe use of flash calcined kaolin clay as a filler to fully or partiallyreplace the titanium dioxide filler which is typically used as anopacifier in polyolefin polymer compositions, and products or articlesformed therefrom. The invention also relates to methods of making suchcompositions, to products such as films formed from the polymericcompositions and to methods of making such products.

BACKGROUND OF THE INVENTION

The ability of a pigmented or filled polymer system to diffuse andreflect a portion of the incident light is known as its scatteringpower. The scattering power of a pigment or filler is directly linked toits hiding and opacifying power. The scattering power of a filler orpigment is related to two properties, refractive index and particle sizedistribution. The greater the difference between the refractive indexesof polymer and pigment or filler the greater the scattering power, andtherefore the greater the opacity. TiO₂ rutile, with the highestrefractive index of all common pigments (of the order of 2.55 foranatase and 2.7-2.75 for rutile), is the most efficient scatterer and iswell known as an opacifying white pigment for polyolefin polymers, andin particular polyethylene products such as polyethylene film. However,titanium dioxide is an expensive material and so it would be desirableto be able to replace some or all of the titanium dioxide in polyolefinapplications. In this respect, one known replacement, or partialreplacement, opacifier is particulate calcium carbonate.

U.S. Pat. No. 5,571,851 describes the use of silane treated calcinedclays as reinforcing fillers for plastics systems such as polyamides.

Flash calcined kaolin clay, which is made by a process in which ahydrous kaolin clay is exposed to an elevated temperature for a shortperiod of time, for example a few seconds, is already known as a fillerfor elastomer compositions, see GB-A-2067535. Flash calcined clay hasalso been used for many years as an extender for titanium dioxide inpaints (WO 99/24360).

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention, there is provideda polymer composition comprising a polymer resin, an amount of a flashcalcined kaolin clay filler and an amount of a titanium dioxide filler,wherein the weight ratio of the flash calcined clay to the titaniumdioxide in the composition is in the range of up to 10:1 and wherein thepolymer resin is one which hardens or cures to a plastic material whichhas a refractive index of at least about 1.45.

The polymer composition may be prepared as a masterbatch composition,which may then be “let down” to an appropriate filler content beforeformation of the final polymeric product, such as a film product, fromthe polymer composition.

According to a second aspect of the invention, there is provided aproduction process for preparing a polymer composition of the firstaspect of the invention in which the flash calcined kaolin clay and thetitanium dioxide are mixed with the polymer resin to form a homogenouscomposition.

According to a third aspect of the present invention there is provided apolymer article made from the polymer composition of the first aspect ofthe present invention. For example, the polymer article may be apolyolefin film. Thus, in one embodiment, the present invention relatesto a polyolefin film, preferably a polyethylene film, formed from apolymer composition of the first aspect of the invention.

The use of flash calcined kaolin clay in plastics which have arefractive index of at least about 1.45 permits the amount of titaniumdioxide, which is a relatively expensive raw material, to be reduced,while retaining satisfactory product characteristics, particularly theopacity and whiteness of the product. This is of particular use forproducts such as polyolefin, e.g. polyethylene, film.

Without wishing to be bound by theory, it is believed that therefractive index of particulate flash calcined clay (which has beenmeasured to be of the order of about 1.39) enables it to be used as anopacifier (and particularly as a partial replacement for a proportion ofa titanium dioxide opacifier) in respect of polymer systems which have arefractive index greater than about 1.45, without the particle sizehaving to be unacceptably high.

The term “particle diameter” used herein refers to a particle sizemeasurement as determined by laser light particle size analysis using aCILAS (Compagnie Industrielle des Lasers) 1064 instrument. In thistechnique, the size of particles in powders, suspensions and emulsionsmay be measured using the diffraction of a laser beam, based onapplication of the Fraunhofer theory. The term “mean particle size” or“d₅₀” used herein is the value, determined in this way, of the particlediameter at which there are 50% by volume of the particles which have adiameter less than the d₅₀ value. The preferred sample formulation formeasurement of particle sizes using the CILAS 1064 instrument is asuspension in a liquid. The CILAS 1064 instrument normally providesparticle size data to two decimal places, to be rounded up or down whendetermining whether the requirements of the present invention arefulfilled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows opacity of polyethylene films made in Example 1 as afunction of the level of the flash calcined kaolin clay for film with3.6% TiO₂. The broken line represents the value at 0% flash calcinedclay and 4% TiO₂.

FIG. 2 shows the transmittance of films made in Example 1 containing3.6% by weight TiO₂ as a function of the level of flash calcined clay.The broken line represents the value at 0% flash calcined clay, 4% byweight TiO₂.

FIG. 3 shows the tensile strength (Elongation at break and Stress atbreak) properties in MD of polyethylene films made in Example 1containing 3.6% TiO₂ by weight as a function of the level of flashcalcined clay. The data point at 0% flash calcined clay contains 4%TiO₂.

FIG. 4 shows the opacity of TiO₂:FCC films made in Example 2 as afunction of FCC/TiO₂ ratio, for FCCs with specific gravities rangingfrom 1.99 to 2.19. The total filler loading (TiO₂+FCC) was kept constantat 4 wt. %.

FIG. 5 shows the transmittance of TiO₂:FCC films made in Example 2 as afunction of ratio of FCC to TiO₂ for FCCs with specific gravity rangingfrom 1.99 to 2.18. The total filler loading (TiO₂+FCC) was kept constantat 4 wt. %.

FIG. 6 shows the calculated ΔE values of TiO₂:FCC films of Example 2 asa function of ratio of FCC to TiO₂ for FCCs with specific gravitiesranging from 1.98 to 2.19. The total filler loading (TiO₂+FCC) was keptconstant at 4 wt. %.

FIG. 7 shows tensile strength at break of TiO₂:FCC films of Example 2 asa function of ratio of FCC to TiO₂ for FCCs with specific gravityranging from 1.98 to 2.19. The total filler loading (TiO₂+FCC) was keptconstant at 4 wt. %.

FIG. 8 shows Elmendorf tear strength of TiO₂:FCC films of Example 2 as afunction of ratio of FCC to TiO₂ for FCCs with specific gravity rangingfrom 1.98 to 2.19. The total filler loading (TiO₂+FCC) was kept constantat 4 wt. %.

FIG. 9 shows opacity and transmittance (normalised values) ofLLDPE/TiO₂/FCC films made in accordance with Example 3.

FIG. 10 shows opacity and transmittance (normalised values) ofHDPE/TiO₂/FCC films made in accordance with Example 3.

FIG. 11 shows opacity and transmittance (normalised values) ofPS/TiO₂/FCC films made in accordance with Example 3.

FIG. 12 shows tensile strength properties (MD) of PE films containingTiO₂/FCC blends of Example 3. (In this figure, the elongation at breakof PS films is multiplied by 100.)

FIG. 13 shows Elmendorf tear test properties of PE films containingTiO₂/FCC blends of Example 3.

DETAILED DESCRIPTION OF THE INVENTION

The polymer composition of the invention comprises a polymer resin.“Resin” is the general term used in the plastics art to denote apolymeric material (solid or liquid) prior to shaping into a plasticarticle.

The polymer resin used in the present invention is one which, onhardening (in the case of thermoplastic plastics) or curing (in the caseof thermosetting plastics), forms a plastics material which has arefractive index of at least about 1.45. The refractive index is asmeasured by ASTM D542.

Preferred polymer resins are polyolefin resins, for example homopolymersof an olefin such as ethylene, propylene, butene or the like, orcopolymers of an olefin monomer and another monomer. Typical examples ofpolyolefin homopolymers are polyethylene resins such as low-densitypolyethylene (which has a refractive. index (RI) of 1.51),middle-density polyethylene (RI 1.52) and high-density polyethylene (RI1.54), polypropylene resins, e.g. polypropylene atactic (RI 1.47) orpolypropylene isotactic (RI 1.49), poly(4-methylpentene) resins andpolybutene resins, such as polyisobutylene (RI 1.51). Also suitable foruse in the invention is linear low-density polyethylene (LLDPE) (RI1.51) which although sometimes referred to as a homopolymer of ethyleneis in fact an ethylene-α-olefin copolymer made by copolymerisingethylene with an α-olefin co-monomer, normally butene, hexene or octene.Polyolefin copolymers which may be used in the present invention includepolymers of two or more olefin monomers such as ethylene-polypropylenecopolymer and copolymers of ethylene or propylene with lower olefinssuch as butene-1, pentene-1, hexane or octene, as well as copolymers ofan olefin monomer and another monomer, such as ethylene-vinyl acetatecopolymer (RI 1.47-1.49), ethylene-acrylic acid copolymer,ethylene-methacrylic acid copolymer. Mixtures of two or more differentpolyolefin copolymers are also contemplated, particularly mixes of LDPEand LLDPE.

Above all, polyethylene resins and blends thereof are preferable, andlinear low-density polyethylene (ethylene-α-olefin copolymer) andlow-density polyethylene are most preferable. Typical densities forthese materials are as follows: 0.904 to 0.912 for ULDPE, 0.913 to 0.933for LDPE, 0.915 to 0.942 for LLDPE and 0.949 to 0.964 for HDPE. Typicalmelt flow ratios are as follows: 0.25 up to 150, normally up to 20,typically up to 8 for LDPE; 0.5 up to 50, normally up to 20, andtypically up to 10 for LLDPE; and 0.05 up to 30, normally up to 20 andtypically up to 8 for HDPE.

The polyolefin resins used in the invention may be obtained bypolymerization in a known way, e.g. by the use of a Ziegler catalyst, orobtained by the use of a single site catalyst such as a metallocenecatalyst.

Examples of other plastics materials which may be used in accordancewith the present invention are as follows, together with the refractiveindex where known:

Poly(vinyl acetate) 1.467 Epoxy resins 1.47 Ethyl Cellulose 1.47 AcetalHomopolymer 1.48 Acrylics 1.49 Cellulose Nitrate 1.49-1.51 Polyallomer1.492 Polyvinyl alcohol 1.50 Ionomers 1.51 Nylons (PA) Type II 1.52Acrylics Multipolymer 1.52 Styrene Butadiene Thermoplastic 1.52-1.55 PVC(Rigid) 1.52.-1.55  Nylons (Polyamide) Type 6/6 1.53 Urea Formaldehyde1.54-1.58 Styrene Acrylonitrile Copolymer 1.56-1.57 Polystyrene1.57-1.60 Poly(ethylene terephthalate) 1.575 Polycarbonate (Unfilled)1.586 Polyvinylidene chloride 1.60 Polysulfone 1.633

Preferred amongst these other polymer materials are PVC and epoxyresins. The use of the invention in respect of nylon (6 and 6,6), PETand polystyrene resins are also preferred aspects of the invention.

As previously noted, the polymer composition of the invention includesas a co-opacifier with titanium dioxide, a flash calcined kaolin clay.

Calcined kaolin clay is normally prepared by heat-treating (calcining) ahydrous kaolin clay material. This serves to remove hydroxyl groups fromthe molecular structure (dehydroxylation). The calcination processtypically causes significant modification of the crystal structure ofthe kaolin, leading to modification of the characteristics of thematerial. In particular, when a hydrous kaolin is calcined to about500-600° C., an endothermic reaction occurs. Essentially all of thewater associated with the uncalcined kaolin crystals is eliminated andan essentially amorphous (as measured by x-ray diffraction) materialcalled metakaolin results. If the kaolin is heated to highertemperatures, further significant changes occur. The metakaolinundergoes an exothermic reaction (which typically occurs at about900-980° C.). Such a material is then referred to as a “fully calcinedkaolin”.

The calcined kaolin used in the present invention is prepared by a flashcalcination process, conducted on particles of hydrous kaolin. In theflash calcination process, the hydrous kaolin clay is heated at anextremely fast rate, almost instantaneously, e.g. by exposure to atemperature greater than about 500° C. for a time not more than 5seconds, and typically less than 1 second. The temperature is suitablyin the range of from 550° C. to 1200° C.

Flash calcination of the hydrous kaolin particles (e.g. for less thanabout 1 second, for less than 0.5 second or for less than 0.1 second)gives rise to relatively rapid blistering of the particles caused byrelatively rapid dehydroxylation of the kaolin. Water vapour isgenerated during calcination, which may expand extremely rapidly, infact generally faster than the water vapour can diffuse through thecrystal structure of the particles. The pressures generated aresufficient to produce sealed voids as the interlayer hydroxyl groups aredriven off, and it is the swollen interlayer spaces, voids, or blistersbetween the kaolin platelets which typify flash calcined kaolins andgive them characteristic properties.

The flash calcination process may be carried out by injecting the kaolinclay into a combustion chamber or furnace wherein a vortex isestablished to rapidly remove the calcined clay from the combustionchamber. A suitable furnace would be one in which a toroidal fluid flowheating zone is established. For example, reference is made here toWO-A-99/24360, the contents of which are incorporated by reference intheir entirety.

Following calcination, the flash calcined clay may be comminuted to thedesired fineness and particle size distribution. Comminution may beachieved by use of conventional processing techniques such as sandgrinding (e.g. wet sand grinding in suspension), milling (e.g. dry ballmilling or fluid energy milling), centrifigation, particle sizeclassification, filtration, drying and the like. Wet sand grinding ispreferred, in which case the desired particle size reduction istypically achieved after a work input of about 110 kilowatt-hours pertonne, and the kaolin is then preferably filtered, dried at 80° C. andmilled to provide the final product.

The flash calcined kaolin used in the present invention typically has aspecific gravity lower than hydrous kaolin, for example, equal to orless than 2.4, and desirably equal to or less than 2.2.

The flash calcined kaolin clay used in the invention is in particulateform and may suitably, but not essentially, have a particle sizedistribution such that at least about 40 weight % is below 2 μm, andpreferably up to about 75 weight % is below 2 μm. More preferably, theflash calcined clay has a particle size distribution such that betweenabout 50 and 65 wt. % are smaller than 2 μm. The preferred d₅₀ of theflash calcined clay is in the range of from about 1.4 to 2 μm. Forexample, one presently preferred flash calcined clay for use in theinvention may have about 55 wt. % of particles smaller than 2 μm and ad₅₀ of about 1.7 micron. In addition, the flash calcined clay for use inthe invention may have a surface area in the range of from 5 to 25 m²per gram. (as measured by the BET liquid nitrogen absorption method ISO5794/1), preferably about 10 to 20 m² per gram, and typically of theorder of 12-14 m² per gram.

The particles of the flash calcined kaolin clay used in accordance withthe present invention may be coated with an adherent coupling agent,which is preferably an organosilane coupling agents. Examples ofsuitable organosilane coupling agents include compounds of formula I:

wherein R₁ is an aminoalkyl or mercaptoalkyl group, R₂ is a hydroxy,hydroxyalkyl or alkoxy group, and each of R₃ and R₄, which may be thesame or different, is a hydrogen atom or a hydroxy, alkyl, hydroxyalkylor alkoxy group. Each of R₂, R₃ and R₄ may, for example, be a hydroxy,hydroxyalkyl or alkoxy group, and each of R₁, R₂, R₃ and R₄ may, forexample, contain not more than 4 carbon atoms. In one example, R₁ may bea γ-mercaptopropyl group and each of R₂, R₃ and R₄ may be a methoxygroup.

An alternative representation of examples of suitable organosilanecoupling agents, which to some extent overlaps with formula I, is givenby the following formula II:(R₁O)₂R′—Si—X  (II)wherein R′ represents a C₁₋₄ alkyl (e.g. methyl or ethyl) group, R₁represents a methyl or ethyl group and X represents a mercaptopropylgroup, a vinyl group or a thiocyanatopropyl group.

Still further examples of suitable organosilane coupling agents includecompounds of formula III:(RO)₃—Si—(CH₂)_(m)—S_(k)—(CH₂)_(m)—Si(OR)₃  (III)wherein R represents a C₁₋₄ alkyl (e.g. methyl or ethyl) group and m andk are each independently selected from the integers 1, 2, 3, 4, 5 and 6(e.g. m=3 and k=4).

Still further examples of suitable organosilane coupling agents includecompounds of formula IV:X₃SiR  (IV)wherein X represents a C₁₋₄ alkoxy (e.g. methoxy or ethoxy) group or achlorine atom, and R represents a glycidoxy, methacryl, amino, mercapto,epoxy or imide group.

Examples of preferred silanes for use in the invention areγ-aminopropyltriethoxy and vinyl-tris(2-methoxyethoxy)silane.

Preferably, the organosilane will be present in an amount up to about 2%by weight of the calcined clay particles, more preferably from about 1%to about 1.5% by weight.

In addition to the flash calcined kaolin clay, the polymer compositionof the invention, and products formed from it, also comprise titaniumdioxide in a particlute form as an opacifier and white pigment.Particulate titanium dioxide for use as an opacifier in a polymercomposition and products formed therefrom is widely available.Typically, however, the titanium dioxide used in this invention has amedian aggregate size in the range of from about 0.2 to 0.35 μm (asmeasured by x-ray disc centrifuge). Suitable titanium dioxide productswhich may be used in the invention are the Ti-Pure® range of materialsform Du Pont.

The weight ratio of the flash calcined clay to the titanium dioxide inthe composition should be in the range of up to about 10:1. Moretypically, the weight ratio of flash calcined clay to TiO₂ will be nogreater than about 1:1. The preferred weight ratio of the flash calcinedclay to the titanium dioxide in the composition is from about 1:100 toabout 1:1, more preferably from about 1:25 to about 1:1. The presentlymost preferred range is from about 1:3 to about 1:1.

The polymer composition of the present invention, and plastic productsformed therefrom may additionally comprise other particulate opacifyingpigments, such as zirconium dioxide, zinc sulfide, antimony oxide, zincoxide, lithopone (zinc sulfide+barium sulfate), barium sulfate,dolomite, magnesium silicate, calcium sulfate, calcium carbonate,alumina and quartz.

The polymer composition of the invention will normally be formed as amasterbatch (or concentrate) which is then let down, prior to use in asuitable product-forming step. Masterbatch compositions in accordancewith the present invention may comprise up to 90 wt. % of flash calcinedclay and TiO₂ combined, based on the weight of the masterbatch (g flashcalcined clay and TiO₂ per 100 g of masterbatch), typically from 40 to80 wt. % of the flash calcined clay and TiO₂ based on the weight ofmasterbatch.

Polymer compositions in accordance with the present invention which areto be used directly in a product-forming step may be prepared (let down)from a masterbatch, as described above, or formed directly to theappropriate composition. Such polymer compositions should comprise asufficient amount of flash calcined kaolin clay and TiO₂ to opacify theresultant composition, and the products formed therefrom. Althoughdependent on the polymer and the final application of the product,typically, the polymer composition of the invention which is to beshaped into a plastics article may comprise up to about 30% by weight ofcombined flash calcined clay and TiO₂ opacifiers, preferably up to about10% by weight, and will typically contain at least about 1% by weight ofthe combined flash calcined clay and TiO₂ opacifier. For polyethylenefilm applications, the amount of flash calcined clay and TiO₂ opacifieris preferably in the range of from 1 to 10% by weight.

The polymer compositions of the present invention may comprise furtheradditives, well known in the plastics art. Amongst the further additiveswhich may be included are bonding or tackifying agents, plasticisers,lubricants, anti-oxidants, Ultraviolet absorbers, dyes, colourants,processing stabilisers and processing aids.

The present invention also contemplates polymer compositions, andproducts formed therefrom, which further comprise a predominantparticulate filler material. For example, moisture permeable, or“breathable” polyolefin film, particularly breathable polyethylene andpolypropylene films, comprises a substantial proportion of a inorganicmaterial, normally a calcium carbonate filler, which may be present inan amount of the order of up to about 70 wt. % in the composition fromwhich the film product is formed and in the film itself. It is knownthat such compositions may also comprise an opacifying amount of a TiO₂.In accordance with the present invention, such compositions may alsoinclude a flash calcined clay as a co-opacifier in combination with theTiO₂.

The polymer resin, flash calcined kaolin clay and titanium dioxide and,if necessary, other optional additives, may be formed into a suitablemasterbatch by the use of a suitable compounder/mixer in a manner knownper se, and may be pelletized, e.g. by the use of a single screwextruder or a twin-screw extruder which forms strands which may be cutor broken into pellets. The compounder may have a single inlet forintroducing the flash calcined kaolin clay, the titanium dioxide and thepolymer together. Alternatively, separate inlets may be provided for theopacifier components and the polymer resin. Suitable compounders areavailable commercially, for example from Werner & Pfleiderer.

As an alternative to forming a single masterbatch, the titanium dioxideand the flash calcined clay may be formed into separate masterbatches,which are then combined and made down in suitable proportions to formthe final polymer composition from which the plastics article is to bemade.

The polymer composition of the present invention, having an appropriateconcentration of opacifier for the intended end use, may be shaped in asuitable molding process to form a plastics product. Examples ofplastics products which may be formed from the polymer composition ofthe invention include polyolefin films, and in particular polyethylene(such as LDPE and LLDPE) films, as well as non-film products such asopaque plastic containers, bottles, etc. The present invention isparticularly suited to making plastic film, which may then be used inwide variety of end uses, such as bags, packaging material, wrappingpaper, pouches, agricultural film, etc. Such films typically have athickness which may be in the range of up to 500 μm, more often up to300 μm, and normally in the range of from 20 to 80 μm.

Plastics products may be formed in a wide variety of shaping procedures,such as, for example, extrusion, injection molding, compression molding,blow molding and casting. The preferred plastic films of the presentinvention may, for example, be made by casting the film using a flat dieor by blow molding the film using a tubular die. The polymer compositionof the invention may also be co-extruded into multilayer films withother polymers both in cast and blown film processes. Suitable otherpolymers for co-extrusion in this respect may be nylon, polyethylene(all types), polyvinyl acetate and polyvinyl alcohol, PVC and PVdC, PET,OPP, as well as suitable adhesive layers In extrusion methods for makingplastics film, the film may be extruded onto a set of rollers thatsmooth and stretch the film. This stretching or orientation stage may,for example, be done in MD only, TD only or both using a variety of flatfilm orientation processes such as stretching using flat rollers,inter-digitated rollers, tenter frames or tenter chains. The film maybe, alternatively oriented using tubular orientation processes (which isnormally used for blown film).

In addition the plastic films may be modified to improve surfaceproperties for ease of printing, film lamination, and/or film adhesionusing a selection of processes such as: corona treatment, flametreatment, priming or sub-coating, use of adhesives, solvents orcoatings.

The invention will now be illustrated with reference to the followingnon-limiting examples.

EXAMPLE 1

Polyethylene compositions for film production were prepared from threemasterbatches, a TiO₂ masterbatch nominally comprising 60 wt. % TiO₂, aflash calcined clay (hereafter FCC) LDPE/LDPE (50:50) masterbatchnominally comprising 15 wt. % FCC and a silane treated FCC (hereafterTFCC) LDPE/LDPE (50:50)masterbatch comprising 15 wt. % TFCC. The TiO₂masterbatch was obtained as a commercially available product. The FCCmasterbatch was prepared using a twin screw extruder at an FCC loadingof 15 wt. %, also including an antioxidant in an amount of 0.1 g per 100g of resin. The FCC had a particle size distribution as follows: 4%larger than 10 μm; 5% larger than 8 μm, 12% larger than 5 μm, 55%smaller than 2 μm, 30% smaller than 1 μm, 15% smaller than 0.75 μ m andless than 5% smaller than 0.5 μm, and a typical d₅₀ value of 1.6 μm. TheTFCC masterbatch was prepared in the same way as the FCC masterbatch,using a similar FCC to that used for the FCC masterbatch, coated with 2%by weight γ-propyltriethoxysilane.

Final formulations were obtained by dilution of TiO₂, FCC and TFCCmasterbatches (60%, 15% and 15% by weight respectively) using a twinscrew extruder (Baker Perkins MP2000). The polymer system used to dilutethe masterbatches was the same 50:50 blend of LDPE and LLDPE used toprepare the FCC and TFCC masterbatches. Antioxidant Irganox 1076 (Ciba)was added at 0.10 g per 100 grams of polymer. All compounding was doneat a screw speed of 350 rpm; feed rates to the compounder were adjustedto 8 to 12 kg.h⁻¹ to maintain constant torque and stable processing.Selected temperatures of 190 (die),180, 170, 165, 160 and 155° C. wereused which allowed a melt temperature at the die of 195 to 197 for FCCcompounds and 195 to 201 for TFCC compounds.

Films with a nominal thickness of 50 μm were blown using a Betol SK 32Line with a screw speed of 56 rpm and a layflat width of 225 mm, whichcorresponds to a BUR of 2.8.

A variety of films were prepared as detailed in Table 1 below comprisingmixes of from 2 to 3.6 wt. % TiO₂ and from 0.8 to 2 wt. % FCC (Films 1gto 1g) or TFCC (Films 2b to 2g) together with films comprising 4 wt. %TiO₂ or 4 wt. % FCC (or TFCC). These were nominal loadings; the actualfiller loadings were also measured by loss on Ignition at 650° C. for 1hr. Measurement was repeated 5 times for each film formulation andresults averaged. All filler loadings are given in Table 1 in weightpercentage. The measured filler levels are ±0.4%.

TABLE 1 Film ID TiO₂ FCC Total_(Target) Filler_(measured) 1a 4.0 0.0 4.03.99 1b 3.6 0.4 4.0 3.96 1c 3.6 0.8 4.4 4.52 1d 3.6 1.2 4.8 4.88 1e 3.61.6 5.2 5.28 1f 3.2 0.8 4.0 4.26 1g 2.0 2.0 4.0 4.30 1h 0.0 4.0 4.0 4.332b 3.6 0.4 4.0 4.42 2c 3.6 0.8 4.4 4.82 2d 3.6 1.2 4.8 5.26 2e 3.6 1.65.2 5.37 2f 3.2 0.8 4.0 3.89 2g 2.0 2.0 4.0 5.87 2h 0.0 4.0 4.0 4.41

Film specimens were conditioned at 23° C. and 50% RH for 48 hours priorto optical and mechanical measurements.

Opacity

Measurement of the opacity of films made with the untreatedflash-calcined clay provided the values shown in Table 2 below. Opacitywas measured by the contrast ratio method using a Minolta CM-361Spectrophotometer. Measurements were made using paraffin oil, with arefractive index close to that of LDPE and LLDPE, to eliminate theeffect of surface defects on the film (scratches, due to flowinstabilities, filler protruding from film) on optical properties. Dueto the sensitivity of opacity to film thickness variation the measuredopacity values were normalized to a film thickness of 50 μm.

TABLE 2 Film ID wt % TiO₂ wt % FCC L/μm Opacity Op^(corrected) 1a 4 052.1 68.0 67.3 1b 3.6 0.4 50.0 65.8 65.8 1c 3.6 0.8 50.1 66.7 66.7 1d3.6 1.2 49.4 66.6 66.8 1e 3.6 1.6 47.9 66.3 67.0 1f 3.2 0.8 51.4 66.365.8 1g 2 2 52.1 59.1 — 1h 0 4 48.9 19.3 — 2b 3.6 0.4 49.2 66.3 66.6 2c3.6 0.8 48.4 66.3 66.8 2d 3.6 1.2 49.1 65.9 66.2 2e 3.6 1.6 50.0 66.766.7 2f 3.2 0.8 49.0 62.7 — 2g 2 2 48.4 65.6 — 2h 0 4 51.4 31.0 —

Results are also presented in FIG. 1 which shows opacity as a functionof the level of FCC for film with 3.6% TiO₂. The broken line representsthe value at 0% FCC, 4% TiO₂. These values indicate that, uponreplacement of 10% TiO₂, an amount of FCC 4 times that of the replacedTiO₂ was sufficient recover the opacity value of the original film.

Transmittance/Colour

The transmittance of the films comprising the untreated FCC was alsomeasured to check the opacity data obtained, as were the haze andclarity. The results obtained are set forth in Table 3 below.Transmittance (T), haze (H), and clarity (C) were measured with aBYK-Gardner Haze Gard-plus meter following a method that conforms toASTM D-1003 and D-1044. T_(L) ^(C) is the standardized transmittance fora standard thickness of 50 μm and the target weight of filler. Fillerpercentage are in weight % and L is the thickness of the film inmicrons.

TABLE 3 ID % TiO₂ % FCC L/μm T/% T_(L) ^(C) H C 1a 4.0 0.0 51.3 46.947.8 >99 55.3 1b 3.6 0.4 49.8 48.9 48.8 >99 62.9 1c 3.6 0.8 49.5 48.548.1 >99 56.3 1d 3.6 1.2 49.8 46.5 46.4 >99 49.8 1e 3.6 1.6 49.6 46.946.6 >99 42.0 1f 3.2 0.8 50.9 47.1 47.7 >99 51.4 1g 2.0 2.0 50.8 55.255.7 >99 62.2 1h 0.0 4.0 51.9 87.7 88.1 59.7 57.9 2b 3.6 0.4 49.747.7 >99 65.0 2c 3.6 0.8 49.7 46.0 >99 53.9 2d 3.6 1.2 50.9 47.0 >9959.3 2e 3.6 1.6 50.7 45.6 >99 42.4 2f 3.2 0.8 50.4 51.8 >99 72.2 2g 2.02.0 50.3 48.5 >99 52.4 2h 0.0 4.0 51.4 79.8 78.1 59.5

Results are also presented in FIG. 2 which shows transmittance of filmscontaining 3.6% by weight TiO₂ as a function of the level of FCC. Thebroken line represents the value at 0% FCC, 4% by weight TiO₂. Allvalues are normalised to 50 μm film thickness. Error bars correspond to2 standard deviations. FIG. 2 shows upon replacement of 10% TiO₂ thelevel of transmittance of the original film is recovered when the levelof added FCC is approximately 3 to 4 times that of the substituted TiO₂.Within experimental error this is in agreement with the observations onfilm opacity.

Measurements were also made of the colour of untreated FCC-filled film.Colour was measured using Minolta CM-361 Spectrophotometer. Colourmeasurements of TiO₂/FCC films are set forth in Table 4 below. ΔEcorresponds to Brightness and is calculated from values of L*, a*, andb*.

TABLE 4 ID % TiO₂ % FCC L* a* b* C* h ΔE 1a 4.0 0.0 96.9 −0.13 2.44 2.4593.0 3.97 1b 3.6 0.4 96.5 −0.11 2.6 2.60 92.5 4.39 1c 3.6 0.8 96.3 −0.092.65 2.65 92.0 4.57 1d 3.6 1.2 95.8 −0.08 2.78 2.78 91.6 5.05 1e 3.6 1.695.6 −0.05 2.94 2.95 91.0 5.32 1f 3.2 0.8 96.2 −0.09 2.66 2.66 92.0 4.681g 2.0 2.0 95.0 −0.02 3.14 3.14 90.4 5.92 1h 0.0 4.0 87.6 0.19 5.34 5.3587.9 13.5

Table 4 shows colour parameters for all films containing FCC. Referenceto this table illustrates that the addition of FCC to substitute theTiO₂ increases the yellowness of the film, as indicated by the increasein b* values with FCC concentration. Changes in L*, a*, and b* aresummarised when we observe changes in the brightness values, ΔE. Asignificant change in brightness is observed with increasing levels ofadded FCC.

Colour measurements were also made of the treated FCC-filled film. Theresults obtained are set forth in Table 5 below.

TABLE 5 ID % TiO₂ % FCC L* a* b* C* h ΔE 2b 3.6 0.4 96.5 −0.14 2.47 2.4893.3 4.31 2c 3.6 0.8 96.4 −0.13 2.67 2.67 92.9 4.46 2d 3.6 1.2 96.1−0.14 2.65 2.66 93.0 4.72 2e 3.6 1.6 96.2 −0.13 2.88 2.88 92.5 4.78 2f3.2 0.8 96.6 −0.14 2.68 2.69 93.1 4.36 2g 2.0 2.0 96.0 −0.13 2.92 2.9392.6 4.93 2h 0.0 4.0 92.6 −0.19 4.52 4.53 92.4 8.66

A yellowing test for discolouration at 85° C. in the presence ofnitrogen oxides was also conducted on the untreated FCC films. Theresults of this test (not shown) indicate that after a 2-hour periodexposure to NO_(x) gasses none of the samples showed discoloration.

Mechanical Properties

The mechanical properties of the films were also measured to determinewhether these are affected by the level of substitution of TiO₂. Tensilestrength was measured according to ASTM D 882-91. The results obtainedare set forth in Tables 6 (tensile properties of films in machinedirection) and 7 (tensile properties of films in transverse direction)below

TABLE 6 ID TiO₂ CC L/μm El/% Error S_(b)/MPa Error BF/Nm⁻¹ Error 1a 4.00.0 51.2 643 27 28.4 2.5 1456 125 1b 3.6 0.4 50.7 602 13 25.2 1.6 1300128 1c 3.6 0.8 50.8 611 27 24.8 1.8 1259 106 1d 3.6 1.2 51.1 571 15 24.51.2 1254 99 1e 3.6 1.6 53.8 582 38 25.3 1.7 1357 68 1f 3.2 0.8 48.7 61912 25.8 1.1 1260 94 1g 2.0 2.0 50.5 555 22 29.3 2.1 1478 91 1h 0.0 4.049.7 556 12 29.9 1.9 1486 105 2b 3.6 0.4 52.4 634 24 27.5 1.5 1442 1032c 3.6 0.8 56.2 636 38 25.8 1.9 1456 233 2d 3.6 1.2 54.5 636 11 26.0 1.51420 141 2e 3.6 1.6 59.0 654 27 26.5 2.2 1570 194 2f 3.2 0.8 55.6 614 1026.0 1.4 1449 155 2g 2.0 2.0 57.3 647 22 25.1 1.6 1443 155 2h 0.0 4.057.5 582 27 25.1 1.7 1441 73

TABLE 7 ID TiO₂ CC L/μm El/% Error S_(b)/MPa Error BF/Nm⁻¹ Error 1a 4.00.0 51.1 609 37 22.7 2.4 1154 126 1b 3.6 0.4 53.3 597 18 20.6 1.6 1105114 1c 3.6 0.8 50.9 584 40 20.8 2.2 1060 111 1d 3.6 1.2 52.1 586 27 20.11.3 1048 67 1e 3.6 1.6 52.5 608 31 22.2 1.7 1162 83 1f 3.2 0.8 50.8 62326 23.8 1.1 1209 81 1g 2.0 2.0 51.1 571 23 25.9 1.7 1324 139 1h 0.0 4.048.9 554 34 26.1 2.7 1280 188 2b 3.6 0.4 54.0 595 22 22.6 1.7 1222 1542c 3.6 0.8 55.3 607 33 22.0 0.6 1218 102 2d 3.6 1.2 54.3 599 27 22.5 1.31227 142 2e 3.6 1.6 54.8 594 42 22.2 2.4 1224 206 2f 3.2 0.8 55.6 615 1126.1 1.5 1453 157 2g 2.0 2.0 52.9 587 38 19.7 2.6 1040 156 2h 0.0 4.057.1 563 43 18.6 2.1 1063 156

Reference to FIG. 3 shows that the mechanical properties of the filmsare not affected by the level of substitution of TiO₂. This is the casefor all tensile properties in both MD and TD. The values are verysimilar for films with compositions varying from 4% TiO₂ to 4% FCC. Thisfact reflects the dominant effect of the resin in the tensile propertiesof these films where it represents 98 to 99% by volume.

In this example it is shown that FCC and silane-treated FCC may be usedas a substitute for TiO₂ in plastic film. At 10% substitution it ispossible to recover the opacity and transmittance of the original 4%TiO₂ film by adding extra FCC to the film (3 to 4 times that of thereplaced TiO₂). Haze is not affected and remains very high. A slightdeterioration of colour and clarity is observed. However, addition ofFCC does not affect the resistance of the film to discoloration.Mechanical properties of the film are not affected by FCC addition.

EXAMPLE 2

Four different flash calcined clays (FCC1, FCC2, FCC3 and FCC4 havingspecific gravities of 2.08, 2.19, 2.03 and 1.98 respectively) werecompounded into LLDPE having a MFI of 20 using a twin-screw extruder(Baker Perkins MP200) to produce 40 wt. % masterbatches. The processingconditions are set forth in Table 8 below.

TABLE 8 Temperature/° C. Torque/ Masterbatch ID Die 5 4 3 2 1 % FCC1 (SG= 2.08) 200 188 177 162 165 150 30 FCC2 (SG = 2.19) 200 188 177 162 165150 30 FCC3 (SG = 2.03) 205 190 178 185 170 165 25 FCC4 (SG = 1.98)% 201177 170 164 165 160 25

All Masterbatches were prepared in Exxon Escorene LLDPE resin LL6101 XR(MFI=20, density 0.924), with antioxidant Irganox1076 added at 0.15 gper 100 g resin. Processing with selected temperatures of 190 (die),180, 170, 165, 155, and 145° C. Extruder operating at 350 rpm except forFCC4, for which a screw speed of 300 rpm was employed. Throughput was inthe range 6 to 8 kg/hr.

These masterbatches, together with a TiO₂ masterbatch, were let downwith Exxon Escorene LLN1001XV (MFI of 1) to achieve a total fillerconcentration (FCC and TiO₂) of 4 wt % using a Baker Perkins twin screwextruder operating at 350 rpm and a throughput in the range 10 to 14kg/hr and selected temperatures of 190 (die), 180, 170, 165, 155, and145° C. For each FCC, compounds were prepared having the following FCCto TiO₂ ratios: 40:30, 30:40, 43:27 and 45:25. Filler loading wasmeasured by loss on ignition at 650° C., except for TiO₂/CaCO₃ films forwhich 450° C. was used. Irganox 1016 was added as a stabiliser at alevel of 0.15 g antioxidant per 100 g of resin. Film processing wascarried out using a Betol SK 32 operating at a screw speed of 56 rpm (10A load) and a haul-off rate of 7 m/min. Film was made at a nominalthickness of 50 micron, and a lay-flat of 225 mm.

Film specimens were conditioned at 23° C. and 50% RH for 48 hours priorto optical and mechanical measurements as in Example 1.

Opacity

The opacity of the TiO₂:FCC films as a function of FCC/TiO₂ ratio forFCCs with SGs ranging from 1.99 to 2.19 was measured and the results areshown in FIG. 4. All films contain 4 wt. % total filler content. Theopacity values are not corrected for filler loading or film thicknessand are, therefore, subjected to relatively large errors (±1-2 opacityunits).

Transmittance/Colour

Transmittance was also measured as in Example 1 and the results,obtained for the same films as in FIG. 4 are illustrated in FIG. 5.Transmittance values are corrected for thickness and filler loading.These values were normalised to a film thickness of 50 μm and a totalfiller loading of 4 wt %. FIG. 5 shows that the reported values aresubjected to large errors (this is also evidenced during normalisationof the values for thickness and concentration).

Colour measurements were also made of the films and the results aresummarised in FIG. 6, which shows the calculated ΔE (which takes accountof L, a and b values) of TiO₂:FCC films as a function of the ratio ofFCC to TiO₂ for FCCs with specific gravity ranging from 1.98 to 2.19.The composition of films was as for FIG. 4. These results show thatincreasing the level of TiO₂ substitution decreases brightness andincreases b values (yellowness).

Mechanical Properties

In order to determine the mechanical properties of the films, thetensile strength and Elmendorf tear strength were measured according toASTM D 882-91 and ASTM D 1922-94a respectively. QUV (UVA) testing wasconducted according to ASTM D 4329-92.

FIG. 7 shows tensile strength at break of TiO₂:FCC films as a functionof ratio of FCC to TiO₂ for FCCs with specific gravity ranging from 1.98to 2.19. The composition of films was as for FIG. 4. In FIG. 7, the lefthand bar of each group corresponds to FCC1, the left middle barcorresponds to FCC2, the right middle bar corresponds to FCC3 and theright hand bar corresponds to FCC4. Error bars correspond to 2 standarddeviations. Within experimental error, tensile strength is not affectedby partial substitution of TiO₂ by FCC. In addition, reference to FIG. 7also shows that the SG of the clay has no effect on tensile strength.

FIG. 8 shows Elmendorf tear strength of TiO₂:FCC films as a function ofratio of FCC to TiO₂ for FCCs with specific gravity ranging from 1.98 to2.19. Again, the composition of films was as for FIG. 4. In FIG. 8, theleft hand bar of each group corresponds to FCC1, the left middle barcorresponds to FCC2, the right middle bar corresponds to FCC3 and theright hand bar corresponds to FCC4. Error bars correspond to 2 standarddeviations. As with tensile strength partial substitution of TiO₂ by FCChas no significant effect on tear strength.

EXAMPLE 3

In this example, the performance of FCC as a partial replacement forTiO₂ in two further polymer systems (HDPE having a refractive index of1.54 and a general purpose polystyrene having a refractive index of1.59) was evaluated and compared with the results from an additionalexperiment using LLDPE.

The polymer systems used were:

-   -   LLDPE Escorene LL6101XR for masterbatch Escorene LLN1001XV for        film blowing    -   HDPE HTA002    -   PS Styron 648

The TiO₂ used was KRONOS 2500, a rutile-based pigment from KronosInternational Inc. The FCC used had a specific gravity of 1.95 asmeasured by apparent density.

Masterbatches of FCC and Kronos 2500, at 30 and 50 wt. %, respectivelywere prepared in each resin type. For LLDPE, LDPE and PS a 3 wt.masterbatch of an appropriate antioxidant was also prepared. IrganoxHP2215FF was used for LLDPE and HDPE, whereas Irganox 1076 was used forPS (both anti-oxidants from Ciba Specialty Chemicals). Compounds weremade in a twin screw extruder (Baker Perkins 2000) operating at 300 rpmscrew speed. Temperatures were selected to give melt values of 150° to180° C. in the feeding zone, and 190° to 205° C. at the die. Throughputrates were chosen to give a torque between 30 and 50%. All compoundswere dried in a Conair dryer/desiccator at 60° C. for 8 hr.

Final film formulations were prepared by tumble-mixing appropriateamounts of the masterbatches and unfilled resins. These mixtures werekept dried in a Conair dryer/desiccator for at least 8 hr at 60° C.Films were then blown in a Dr. Collin blown film line. Screw speed was75 rpm in all cases, with drive-off values of 4.6 m min⁻¹ for LLDPE andHDPE, and 10 m min⁻¹ for PS. Processing conditions were chosen to givedie melt temperatures and melt pressures of ca. 205° C. and 340 bar forLLDPE, ca. 215° C. and 310 bar for HDPE, and ca. 205° C. and 210 bar forPS. Polyethylene films were produced with a nominal thickness of 50 mmand a lay-flat of 225 mm. PS films had a nominal thickness of 25 mm, anda lay-flat of 230-250 mm.

Actual filler loading was measured by LOI at 650° C. for 1 hr in a CEMmicrowave furnace. Opacity was measured in films of known thickness bythe contrast ratio with Minolta CM-361 spectrophotometer, using a 10°measurement angle and standard North sky daylight illumination as lightsource. Haze, clarity and transmittance were measured in films of knownthickness using a Gardner Haze meter following ASTM D-1003 and D-1044.Where possible (Transmittance and Opacity) values were standardised tonominal thickness and nominal filler loading, numerically (fortransmittance) or via calibration graphs (for opacity). Colour wasmeasured with a Minolta CM-361 spectrophotometer, using standard 6500 Killumination as the light source and a 10° measurement angle.

Tensile strength was measured according to ASTM D 882-91, using 80mm-long test pieces both in MD and TD for the PE grades, with a strainrate of 800 mm min−1, and a strain rate of 8 mm min−1 for PS. Elmendorftear strength was measured according to ASTM D 1922-4a.

The optical and mechanical properties of the films are set forth inTables 9 and 10 respectively:

TABLE 9 Description Filler/% Op T H C L a* b* OpL, C TL, C LLDPE, 4%TiO₂ 4.6 69.2 42.0 >99 41.8 97.0 −0.39 2.01 67.3 46.1 LLDPE, 3.6% TiO₂,0.4% FCC 3.8 62.6 47.8 >99 74.6 97.2 −0.37 2.04 63.1 47.3 LLDPE, 3.6%TiO₂, 0.8% FCC 4.9 70.1 42.7 >99 39.2 97.1 −0.4 2.02 68.2 46.9 LLDPE,3.6% TiO₂, 1.2% FCC 4.9 69.3 43.8 >99 41.3 96.9 −0.38 2.08 68.7 45.3HDPE, 4% TiO₂ 4.0 68.6 44.2 >99 1.6 98.3 −0.46 1.9 68.9 44.1 HDPE, 3.6%TiO₂, 0.4% FCC 4.7 70.6 42.3 >99 0.8 97.9 −0.44 2.03 66.0 48.1 HDPE,3.6% TiO₂, 0.8% FCC 4.8 67.2 47.1 >99 1.8 97.6 −0.39 2.1 64.5 50.3 HDPE,3.6% TiO₂, 1.2% FCC 5.4 69.6 44.1 >99 1.1 97.3 −0.37 2.19 65.9 48.6 PS,4% TiO₂ 4.6 58.9 51.7 >99 91.3 96.8 −0.34 1.73 53.6 60.4 PS, 3.6% TiO₂,0.4% FCC 4.4 52.7 60.2 95.9 94.5 96.4 −0.37 1.76 52.0 62.5 PS, 3.6%TiO₂, 0.8% FCC 5.2 53.6 58.1 99.0 89.8 96.3 −0.37 1.8 50.7 63.3 PS, 3.6%TiO₂, 1.2% FCC 4.4 53.3 61.0 95.8 89.5 95.9 −0.41 1.77 56.0 58.5Op—opacity; T—transmittance; H—haze; C—clarity; OpL, C—opacitynormalised for thickness and filler loading; TL, C—as for normalisedopacity.

TABLE 10 Tensile Strength in MD Tensile Strength in TD Tear in MD Tearin TD Stress/ BF/ Stress/ F/W/N F/W/N Description MPa Elo./% Nm⁻¹ MPaElo./% BF/N m⁻¹ Force/N mm⁻¹ Force/N mm⁻¹ LLDPE, 4% TiO₂ 33.0 666 158326.2 651 1322 5.31 105.3 5.40 108.6 LLDPE, 3.6% TiO₂ 0.4% FCC 28.0 6001320 22.1 579 1045 4.62 99.0 5.14 107.4 LLDPE, 3.6% TiO₂ 0.8% FCC 27.0614 1358 23.1 602 1117 5.04 103.7 5.61 110.8 LLDPE, 3.6% TiO₂ 1.2% FCC25.8 595 1220 22.3 588 1100 4.83 99.4 5.21 106.3 HDPE, 4% TiO₂ 37.0 5591742 32.5 553 1418 5.62 111.1 8.82 193.3 HDPE, 3.6% TiO₂ 0.4% FCC 31.3466 1336 29.5 505 1321 4.35 99.2 8.77 184.4 HDPE, 3.6% TiO₂ 0.8% FCC33.9 445 1539 30.8 536 1379 4.75 101.0 8.40 191.9 HDPE, 3.6% TiO₂ 1.2%FCC 33.7 438 1543 28.4 485 1302 5.28 117.4 8.35 194.1 PS, 4% TiO₂ 47.22.68 1241 PS, 3.6% TiO₂ 0.4% FCC 53.5 2.85 1228 PS, 3.6% TiO₂ 0.8% FCC49.4 2.61 1186 PS, 3.6% TiO₂ 1.2% FCC 50.8 2.81 1216 Tensile Strength:stress at break (MPa), Elongation at break (% original length), Breakingfactor (N m⁻¹), Trouser tear test (Elmendorf) Maximum force (N), Maximumforce/width (N mm⁻¹).

Opacity and transmittance of all films are summarised in FIGS. 9 to 11based on the data in Table 9. These values have been normalised, byinterpolation, to the average film thickness and filler loading of thefilms to be compared. For HDPE films the values are reported asmeasured. All values and other properties are listed in the appendix inTable 2.

The LLDPE, HDPE, and PS films of this example contained 3.6% by weightTiO₂ and various levels of FCC, which corresponded to replaced TiO₂ :added FCC ratios of 1:1, 1:2, and 1:3. The horizontal line correspondedto the reference material, which in each polymer system contained 4% byweight TiO₂.

FIG. 9 shows the opacity and transmittance of LLDPE films. The resultsindicate that the opacity (or transmittance) was recovered when thelevel of FCC addition was around 2 times that of the replaced TiO₂.

For HDPE (FIG. 10), due to large errors in the measurements it was notpossible to give a precise value of the ratio needed to obtainequivalent opacity to the reference film. However, the values indicatedthat the opacity and transmittance of the studied films are of the sameorder as those of the LLDPE films.

Opacity and transmittance values of PS films (see FIG. 11) showed thatthese were recovered when the ratio was between about 1:1 and about 1:3.

The colour values of the PE and PS films containing TiO₂/FCC blends aresummarised in the following table, Table 11.

TABLE 11 Description L a* b* DE LLDPE 4% TiO2 97.0 −0.39 2.01 3.65 LLDPE3.6% TiO₂ 0.4% FCC 97.2 −0.37 2.04 3.48 LLDPE 3.6% TiO₂ 0.8% FCC 97.1−0.40 2.02 3.58 LLDPE 3.6% TiO₂ 1.2% FCC 96.9 −0.38 2.08 3.75 HDPE 4%TiO₂ 98.3 −0.46 1.90 2.59 HDPE 3.6% TiO₂ 0.4% FCC 97.9 −0.44 2.03 2.96HDPE 3.6% TiO₂ 0.8% FCC 97.6 −0.39 2.10 3.24 HDPE 3.6% TiO₂ 1.2% FCC97.3 −0.37 2.19 3.50 PS 4% TiO₂ 96.8 −0.34 1.73 3.66 PS 3.6% TiO₂ 0.4%FCC 96.4 −0.37 1.76 4.03 PS 3.6% TiO₂ 0.8% FCC 96.3 −0.37 1.80 4.16 PS3.6% TiO₂ 1.2% FCC 95.9 −0.41 1.77 4.48

Reference to this table showed that in all cases, increasing the levelof FCC made the film a bit more yellow and slightly less bright. The avalues were not significantly changed in LLDPE, become slightly lessgreen in HDPE and slightly greener in PS. In addition, PS films wereslightly less yellow than either LLD or HDPE. This may in part beexplained by the slightly blue-ish tone of the PS resin compared to LLDor HDPE. A comparison of the reference films with 1:1 substituted filmsshowed that colour differences were small.

The mechanical properties of the films from Table 10 are displayedgraphically in FIG. 12 and FIG. 13. Elmendorf tear strength of PS filmswas not measured. These results show that, within experimental error(error bars shown correspond to ±2 standard deviations), the addition ofFCC as a partial replacement of TiO₂ did not significantly changemechanical performance when compared with the reference 4% TiO₂ film, inall three of the polymer systems.

All references cited herein are expressly incorporated by reference forall purposes.

The foregoing broadly describes the present invention, withoutlimitation. Variations and modifications as will be readily apparent toone of ordinary skill in this art are to be considered as includedwithin the scope of this application and any subsequent patent(s).

1. A polymer composition comprising a polymer resin, a flash calcinedkaolin clay filler and a titanium dioxide filler, wherein a weight ratioof the flash calcined clay to the titanium dioxide in the composition isin an amount less than or equal to about 10:1 and wherein the polymerresin has a refractive index of greater than or equal to about 1.45 whenhardened and/or cured to a plastic material.
 2. The compositionaccording to claim 1, wherein the polymer resin is a polyolefin resin.3. The composition according to claim 2, wherein the polyolefin resin ischosen from homopolymers of ethene, propene and butene, and copolymersof ethane, propene, butene, and another monomer.
 4. The compositionaccording to claim 3, wherein the polyolefin resin is a polyethyleneresin.
 5. The composition according to claim 4, wherein the polyethyleneresin is chosen from one or more of low density polyethylene, linearlow-density polyethylene, middle-density polyethylene, and high densitypolyethylene.
 6. The composition according to claim 5, wherein thepolyethylene resin is chosen from one or more of low-densitypolyethylene and linear low density polyethylene.
 7. The compositionaccording to claim 1, wherein the polymer resin is a polyvinyl chlorideresin.
 8. The composition according to claim 1, wherein the flashcalcined clay has a specific gravity less than or equal to about 2.4. 9.The composition according to claim 8, wherein the flash calcined clayhas a specific gravity less than or equal to about 2.2.
 10. Thecomposition according to claim 1, wherein the flash calcined clay has aparticle size distribution such that at least 50 weight % of theparticles are smaller than 2 μm.
 11. The composition according to claim1, wherein the flash calcined clay has a particle size distribution suchthat from about 40 weight % to about 80 weight % of the particles aresmaller than 2 μm.
 12. The composition according to claim 1, wherein theflash calcined clay has a d₅₀ ranging from about 1.4 μm to about 2.0 μm.13. The composition according to claim 1, wherein the flash calcinedclay has a specific gravity of less than or equal to about 2.4, aparticle size distribution such that from about 50 weight % to about 65weight % of the particles are smaller than 2 μm, and a d₅₀ ranging fromabout 1.4 μm to about 2.0 μm.
 14. The composition according to claim 1,wherein the flash calcined clay is obtained by exposing a particulatehydrous kaolin clay to a temperature of greater than or equal to about500° C. for a time less than or equal to 5 seconds.
 15. The compositionaccording to claim 1, wherein the flash calcined clay is coated with anadherent coupling agent.
 16. The composition according to claim 15,wherein the adherent coupling agent is an organosilane coupling agent.17. The composition according to claim 1, wherein the titanium dioxidehas a median aggregate size ranging from about 0.2 μm to about 0.35 μm.18. The composition according to claim 1, wherein the weight ratio ofthe flash calcined clay to titanium dioxide ranges from about 1:100 toabout 1:1.
 19. The composition according to claim 18, wherein the weightratio of the flash calcined clay to titanium dioxide ranges of fromabout 1:25 to about 1:1.
 20. The composition according to claim 19,wherein the weight ratio of the flash calcined clay to titanium dioxideranges from about 1:3 to about 1:1.
 21. The composition according toclaim 1, wherein the flash calcined clay and titanium dioxide arepresent in a combined amount up to and including about 80%, by weightrelative to the total weight of the composition.
 22. The compositionaccording to claim 21, wherein the flash calcined clay and titaniumdioxide are present in a combined amount ranging from about 40% to about80%, by weight relative to the total weight of the composition.
 23. Thecomposition according to claim 21, wherein the flash calcined clay andtitanium dioxide are present in a combined amount less than or equal toabout 30%, by weight relative to the total weight of the composition.24. The composition according to claim 23, wherein the flash calcinedclay and titanium dioxide are present in a combined amount ranging fromabout 1% to about 10%, by weight relative the total weight of thecomposition.
 25. The composition according to claim 1, furthercomprising an additional inorganic filler.
 26. The composition accordingto claim 25, wherein the additional inorganic filler is a calciumcarbonate.
 27. The composition according to claim 1, wherein the polymerresin is chosen from nylon 6, nylon 6,6, poly(ethylene) terephthalate,polyvinyl chloride, and polystyrene.
 28. The composition according toclaim 27, wherein the polymer resin is a polystyrene resin.
 29. Apolymer composition comprising a polyethylene resin, a flash calcinedkaolin clay and a titanium dioxide, wherein the weight ratio of theflash calcined clay to the titanium dioxide ranges from about 1:100 toabout 1:1.
 30. The composition according to claim 29, wherein the weightratio of the flash calcined clay to titanium dioxide ranges from about1:25 to about 1:1.
 31. The composition according to claim 30,wherein theweight ratio of the flash calcined clay to titanium dioxide ranges fromabout 1:3 to about 1:1.
 32. The composition according to claim 29,wherein the flash calcined clay and titanium dioxide are present in acombined amount less than or equal to about 80%, by weight relative tothe total weight of the composition.
 33. The composition according toclaim 32, wherein the flash calcined clay and titanium dioxide arepresent in a combined amount ranging from about 40% to about 80%, byweight relative to the total weight of the composition.
 34. Thecomposition according to claim 32, wherein the flash calcined clay andtitanium dioxide are present in a combined amount less than or equal toabout 30%, by weight relative to the total weight of the composition.35. The composition according to claim 32, wherein the flash calcinedclay and titanium dioxide are present in a combined amount ranging fromabout 1% to about 10%, by weight relative to the total weight of thecomposition.
 36. A process for forming a plastic article comprisingcombining a polymer resin, a flash calcined kaolin clay filler and atitanium dioxide filler, wherein the weight ratio of the flash calcinedclay to the titanium dioxide in the composition is in an amount lessthan or equal to about 10:1 and wherein the polymer resin has arefractive index of greater than or equal to about 1.45 when hardenedand/or cured to form the plastic article.
 37. The process according toclaim 36, wherein the plastic article is a polyolefin film.
 38. Theprocess according to claim 36, wherein the plastic article is apolyethylene film.
 39. The process according to claim 36, wherein theplastic article is a polystyrene film.
 40. A process for preparing apolymer composition comprising a polymer resin, a flash calcined kaolinclay filler and a titanium dioxide filler, wherein a weight ratio of theflash calcined clay to the titanium dioxide in the composition is in anamount less than or equal to about 10:1 and wherein the polymer resinhas a refractive index of greater than or equal to about 1.45 whenhardened and/or cured to a plastic material, comprising combining thepolymer resin, the flash calcined kaolin clay and the titanium dioxideto form a homogenous composition.
 41. The process according to claim 40,wherein the flash calcined kaolin clay and the titanium dioxide aremixed with the polymer resin to form a homogenous composition.
 42. Theprocess according to claim 41, wherein separate premixes of (a) thepolymer resin and flash calcined clay and (b) the polymer resin and thetitanium dioxide are formed, and then combined, optionally together withan additional polymer resin.
 43. A polymer composition comprising apolyolefin resin and an opacifying amount of a mixture of titaniumdioxide and a flash calcined kaolin clay.
 44. A polyolefin filmcomprising an opacifying amount of a mixture of a flash calcined clayand titanium dioxide.
 45. A plastic article comprising a polymercomposition, said polymer composition comprising a polymer resin, aflash calcined kaolin clay filler and a titanium dioxide filler, whereinthe weight ratio of the flash calcined clay to the titanium dioxide inthe composition is in an amount less than or equal to about 10:1 andwherein the polymer resin has a refractive index of greater than orequal to about 1.45 when hardened and/or cured to form the plasticarticle.
 46. The plastic article according to claim 45, wherein theplastic article is a polyolefin film.
 47. The plastic article accordingto claim 45, wherein the plastic article is a polyethylene film.
 48. Theplastic article according to claim 45, wherein the plastic article is apolystyrene film.